Fix #311. Add regex to check for field assignment

Author: sigmavirus24

pep8.py

@@ -108,6 +108,7 @@
 KEYWORD_REGEX = re.compile(r'(\s*)\b(?:%s)\b(\s*)' % r'|'.join(KEYWORDS))
 OPERATOR_REGEX = re.compile(r'(?:[^,\s])(\s*)(?:[-+*/|!<=>%&^]+)(\s*)')
 LAMBDA_REGEX = re.compile(r'\blambda\b')
+FIELD_ASSIGNMENT_REGEX = re.compile('\s*.+\..+\s=')
 HUNK_REGEX = re.compile(r'^@@ -\d+(?:,\d+)? \+(\d+)(?:,(\d+))? @@.*$')
 
 # Work around Python < 2.6 behaviour, which does not generate NL after
@@ -872,7 +873,9 @@ def compound_statements(logical_line):
              before.count('[') <= before.count(']') and   # [1:2] (slice)
              before.count('(') <= before.count(')'))):    # (annotation)
             if LAMBDA_REGEX.search(before):
-                yield 0, "E731 do not assign a lambda expression, use a def"
+                if not FIELD_ASSIGNMENT_REGEX.search(before):
+                    yield 0, ("E731 do not assign a lambda expression, use a"
+                              " def")
                 break
             if before.startswith('def '):
                 yield 0, "E704 multiple statements on one line (def)"

testsuite/E73.py

@@ -5,3 +5,6 @@
 #: E731:2:5
 while False:
     this = lambda y, z: 2 * x
+#: Okay
+f = object()
+f.method = lambda: 'Method'